Optoelectronic components on an organic basis, for example organic light emitting diodes (OLEDs), are being increasingly widely used in general lighting, for example as a surface light source.
An organic optoelectronic component, for example an OLED, may include on a carrier an anode and a cathode with an organic functional layer system therebetween. The organic functional layer system may include one or a plurality of emitter layer(s) in which electromagnetic radiation is generated, one or a plurality of charge generating layer structure(s) each composed of two or more charge generating layers (CGL) for charge generation, and one or a plurality of electron blocking layers, also designated as hole transport layer(s) (HTL), and one or a plurality of hole blocking layers, also designated as electron transport layer(s) (ETL), in order to direct the current flow.
A current flow between the electrodes leads to the generation of electromagnetic radiation in the organic functional layer system. The electromagnetic radiation can be extracted from the OLED by means of total internal reflection within the components normally only to the extent of ˜20% without technical aids. The total internal reflection in the OLED can be reduced by means of the use of scattering layers, for example with a scattering layer between the first electrode and the carrier. A higher proportion of the generated electromagnetic radiation, for example light, can be extracted as a result.
In a conventional scattering layer, an organic matrix is used (as a result of which said scattering layer is also designated as an organic scattering layer), in which scattering centers having a different refractive index than the organic matrix are embedded. However, upon contact with water and/or oxygen, organic scattering layers can age or degrade and thus reduce the stability of an OLED. A further disadvantage of organic scattering layers is their low refractive index (n˜1.475). Since the organic functional layer structure usually has a layer-thickness-averaged refractive index of approximately 1.7, with the low refractive index of the organic scattering layers this results in moderate angles of incidence for the criterion of total internal reflection at the interface between the first electrode and the scattering layer, such that the extraction efficiency is moderate.
Furthermore, conventional practice involves cleaning the carrier before forming the scattering layer and cleaning the carrier with scattering layer before forming the first electrode, as a result of which the production method for forming the optoelectronic component becomes more time- and cost-intensive.
Furthermore, conventional organic scattering layers can be readily susceptible to mechanical abrasion on account of the interface between the carrier and the scattering layer. The organic scattering layer can furthermore be damaged in subsequent coating and/or cleaning processes, for example by solvents.
Furthermore, scattering layers composed of high refractive index glass solder with embedded scattering centers are known. The number density of the scattering centers in these scattering layers decreases from the interior to the surface toward the outside or is homogeneous in the layer cross section. Said layer cross section results from the conventional method for producing the layers that are formed from a suspension, or a paste including scattering centers and matrix substance, for example glass solder. However, the roughness of the scattering layer or the form of the scattering centers can lead to the formation of spikes at the scattering layer surface. With the use of scattering particles as scattering centers, scattering particles not completely enclosed by glass at the scattering layer surface can likewise form spikes. Spikes should be understood as local surface roughenings having a high aspect ratio. Particularly in the case of a thin configuration of an OLED, spikes can lead to the first electrode being short-circuited with the second electrode. In addition, during the production of the OLED in direct proximity to the spikes of the scattering layer a local distortion or decrosslinking of the layers on or above the scattering layer can occur, for example of the first electrode or of the organic functional layer. If a thin film encapsulation is applied on the component, then by means of the spikes there is the risk of the thin film encapsulation not being impermeable locally, which can lead to the degradation of the component.
The surface properties of scattering layers, for example a low surface roughness or a defined undulation, are conventionally set by means of a glass layer additionally applied to the scattering layer. This also reduces the risk of scattering particles not completely enclosed by glass being present at the surface of the scattering layer. However, the additional layer usually requires an additional heat treatment step and thus prolongs the process implementation. Furthermore, such a method has the disadvantage that refractive index-changing substances cannot be arranged at the surface of the scattering layer in a controlled manner.
Furthermore, one conventional method is known in which particles are applied to a glass ribbon of float glass while the glass is still hot, such that particles partly sink into the float glass or react chemically therewith. This has the disadvantage, however, that particles of a number of sizes are applied jointly, which can lead to problems mentioned above. In particular, the surface quality (roughness) of the glass can thereby deteriorate since particles cannot be applied in a defined manner and can project in part from the surface.